The invention concerns a gas analyser including a pump unit and autocalibration means.
The invention applies in particular to a gas analyser that is part of a tracer gas leak detector.
Tracer gas leak detectors generally include autocalibration means, i.e. means for calibrating the detector. To this end the device includes a container of tracer gas, generally helium, having a known and calibrated leakage rate.
The container is connected to the inlet of the detector by a valve which is opened during autocalibration. To enable calibration, the calibrated leakage flow is entered into an electronic circuit, for example using thumbwheels on the device, the electronic circuit adjusting the ionisation current of the gas analyser. The device carries a mass selector switch, generally selecting one of three separate possible masses, operating on the ion acceleration voltage. This is so even though the detector contains only one calibrated leakage container for a given gas.
Accordingly, if a tracer gas other than that in the calibrated leakage container inside the device is to be used, it is necessary to use a calibrated leakage cylinder of the other gas and to connect it to the inlet flange of the device and of course to open the device to set the calibrated leakage value of that cylinder on the thumbwheels. The mass selector switch must also be set to the position corresponding to the gas used.
When this has been done, the above parameters (ion acceleration voltage and ionisation current) are adjusted automatically during autocalibration so that the leak shown on the device corresponds to the calibrated leakage flow entered via the thumbwheels.